In order to prevent processing solutions from penetrating into a photographic printing paper support in developing and fixing steps and to reduce processing times including washing and drying times, waterproof supports comprising a raw paper covered with a polyolefin such as polyethylene on both sides have been preferably used for photographic printing paper in recent years.
As for the raw paper, so-called acidic paper has so far been used. The acidic paper is prepared from paper stock to which an anionic sizing agent, an anionic paper-strength reinforcer and a cheap aluminum salt for fixing these anionic chemicals to pulp are added, thereby being rendered acidic.
Recently, however, neutral paper has prevailed as paper for general use because of its advantages, e.g., in having improved durability with respect to paper strength, enabling white water discharged in the paper-making step to be disposed in a closed system, preventing equipment from being corroded, and so on.
In case of raw paper's being used for a photographic printing paper support, it is required thereof to be hard sized paper in order to inhibit a developer from penetrating into the support via the cut surfaces during development. In using neutral paper as the raw paper for a photographic printing paper support, therefore, it becomes necessary to incorporate therein not only an alkylketene dimer having self fixability as sizing agent but also a cationic polyacrylamide as paper strength reinforcer.
The papermaking in the neutral region (6.0.ltoreq. the pH of paper stock .ltoreq.7.5) is inferior to the papermaking in the acidic region (3.5.ltoreq. the pH of paper stock &lt;6.0) in the drainage on wire cloth. Accordingly, the former papermaking has a problem of its suffering an increase in drying load. Further, it has drawbacks that the alkylketene dimer used therein as sizing agent is responsible for stains on rolls such as press rolls and tends to render the raw paper surfaces slippery.
As a result of our intensive studies for solving the above-described problems, it has now been found out that not only the drainage on wire cloth in a papermaking step and squeezability with a wet press can be improved but also a drying load can be reduced when a raw paper is made from the pulp slurry to which (i) as a sizing agent an epoxidized higher fatty acid amide is added in combination with another cationic substance is added and (ii) anionic colloidal silica and/or anionic bentonite is further added after the pulp concentration is controlled so as to range from 0.1 to 1.5%. Moreover, we have found out that the thus made raw paper has excellent smoothness and high paper strength and can considerably reduce the penetration of a developer thereinto via the cut surfaces when it is covered with a polyolefin on the both sides and used as photographic printing paper support, thus achieving the present invention.